Easily the most powerful energy company in the world prior to the Great War, Poseidon Energy was an umbrella corporation with its fingers in virtually all known forms of renewable and non-renewable power sources, so long as they remained profitable.

Though most of the public knew that Poseidon was a huge corporation and never particularly trusted it, very few people were aware that several companies owned by Poseidon were given lucrative defense contracts by the U.S. government – or rather, by Enclave members working as lobbyists to gain those contracts (it seems that some of the Enclave's members were employed by Poseidon as lobbyists). Most of Poseidon’s most promising projects never reached their final stages.

Though technically not part of the Enclave, many powerful corporations benefited from the Enclave’s actions and their research facilities were protected during the atomic firestorm of 2077. Poseidon Energy was chief among these, as its facilities continue to be used by the broken remnants of the Enclave following the Chosen One’s assassination of the Enclave's President and the destruction of their Oil Rig headquarters off of the Pacific coast of California in 2242.

Known Poseidon Energy companies

Poseidon Energy was not a single, monolithic company, but was instead a cartel of various Poseidon-owned corporations controlling various aspects of the global energy market... and cooperating with the Enclave. To facilitate communications (and terminate unlikely hostilities), the PoseidoNet date system provided instantaneous communication between various Poseidon locations.

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Poseidon Oil

Easily the most recognizable of the companies operating under the Poseidon name, PO did not limit itself only to the excavation and pumping of petroleum - it also operated a number of nuclear power plants, one of which was the Reactor No. 5 in Gecko. Major installations belonging to this corporation were the Oil Rig eventually used as the headquarters of the Enclave on the Pacific Ocean and the Navarro refinery on the Pacific coast of California.

Interestingly, Poseidon Oil seems to be a company that had close ties to the Enclave, with it's facilities housing the primary Enclave base after the Great War and Navarro easily converted (or even already existing) into an Enclave military outpost. Also, together with the Enclave, Poseidon helped finance Senator Todd Peterson's secret bunker.

Poseidon Gasoline

Poseidon Gasoline was a company, that before the energy crisis that began in the mid-twenty-first century, apparently operated some network of refueling stations, advertised with road maps for drivers.

Concept art for a gas station

Prometheus Coal

The following is based on Van Buren and has not been confirmed by canon sources.

Prometheus Coal was probably a coal mines operator. At least it opened a coal mine called the Eagle's Rock mine complex in central Utah in 2039. It was eventually sold in 2066 to the U.S. government to serve as a radioactive waste dump.

Other

Due to certain ties to Agricola robot, it is possible that Poseidon took part in the Grand Canyon uranium mining business. It is also likely that numerous other companies operated under the umbrella of Poseidon Energy.

Known Poseidon facilities

"Gecko" power plant

The oil rig 175 miles off the Pacific coast of California was the home base for the Enclave. It is unknown whether the oil drilling platform was originally constructed for this purpose (presumably through a secret military-industrial contract) or was later converted for the Enclave's use. It is also referred to in source files as a "station".

One of Poseidon's atomic power plants, Poseidon Power Plant No. 12, remained in use after the Great War. In the year 2241, Reactor No. 5 was operated by ghouls settled there (they were able to tolerate the low but continuous radiation levels).

The corporation's private data network, PoseidoNet, was still in operation after the Great War, and was used by the Enclave. Its existence was evidence of Poseidon's close links with the federal government before the bombs fell.

Olney Powerworks is stated to be "a division of PPE", which might be one of the branches of Poseidon Energy

The following is based on Van Buren and has not been confirmed by canon sources.

Poseidon-Enclave abandoned projects

Very few people were aware that several companies owned by Poseidon were given lucrative defense contracts by the U.S. government – or rather, by Enclave members working as lobbyists to gain those contracts. Many of Poseidon’s most promising projects never reached their final stages. In their paranoid dreams of a coup against the real U.S. government, the Enclave kept their special toys out of the American military's knowledge until it was too late to actually use them.

After the Great War, Poseidon no longer existed as a real force in the post-atomic world. However, technology scavengers like the Brotherhood of Steel and the Enclave still tried in vain to decipher Poseidon's plans and either confiscate this technology or turn them into working models, respectively.

The following is based on Van Buren and has not been confirmed by canon sources.

There were several unfinished Enclave/Poseidon projects that science-oriented characters could complete (the story behind the projects was planned to help tie the Enclave to Poseidon).

Phoenix - Sub-dermal thermal armor implants, like the ones received in Fallout 2.

Finished products

In the larger Fallout world's background, ODYSSEUS, also known as ULYSSES, was an extremely advanced Artificial Intelligence created by Derek Greenway and developed by Poseidon Energy. Its two names emphasize the difference between Poseidon's Greek names and Greenway's Roman names (see also: Diana).

The T6 Fusion Generator was a sixth-generation TRIDENT-class fusion generator developed by Poseidon Energy. It was relatively large and inefficient, mostly used for the powering of the Vaults and other small, isolated settlements. Present at a malfunctioning Vault in the van Buren tech demo. Despite the fact that Navarro was a Poseidon-owned facility, there were built-in Wattz power generators.